Where it is desired to have a panel such as a motor vehicle interior panel that is soft and resilient, a soft springy material such as plastic foam is commonly employed as a backing for a flexible skin having the desired visual appearance. Fiber batting and fiber preforms made of chopped fibers are also used as the skin backing but to a far lesser degree as they do not possess the soft feel and low spring rate that can be obtained with plastic foam. For processing and other reasons, the foam is commonly made of a thermosetting plastic and while having the above desired attributes, it does have the disadvantage of not being recyclable which is of continuously growing importance. A fiber backing for the flexible skin made of recyclable thermoplastic fibers would be more desirable if such could be provided with spring characteristics comparable to foam on a cost competitive basis. The difficulty resides in combining the fibers in some form and/or manner that will provide and retain a soft springy characteristic when layered between the flexible skin and the rigid retainer.
In the case of fiber batting, the fibers are normally substantially straight and are woven together to form the batting or gathered and held together in an unwoven layered manner to form the batting. In either case, they do not lend themselves to producing a consistent or uniform soft springing action co-extensive with the skin because of their beam like characteristic and bending stiffness. Furthermore, the batting fibers are typically compacted while being bonded or adhered to the flexible skin and this produces an interface stiffness in addition to a structural stiffness that significantly limits the degree of softness that can be felt at the flexible skin.
In the case of a fiber preform, the primary difficulty also resides in stiffness. For example, in making such a preform, it is common practice to spray a layer of chopped fibers onto a foraminous screen through which air is being drawn. The chopped fibers may be precoated with a heat activated binder or the fibers may include binder fibers or a thermoplastic powder may be blown onto the deposited fibers. The chopped fibers are normally substantially straight, are deposited in random orientation on the screen, and are then bonded together with the application of heat to retain the shape of the screen. The chopped fibers on bonding together form a multitrussed structural network of short straight fibers with the result that the chopped fiber preform is relatively stiff and can not be made as soft as foam in forming a springy backing for a flexible skin.